1. Field of the Invention
The present invention relates to the field of inductances and more specifically of inductances of variable value, the inductances being formed from conductive tracks formed, for example, in metallization levels of integrated circuits.
2. Discussion of the Related Art
FIG. 1 is a diagram of an inductance comprising a spiral coil with intermediary taps. Such a coil is conventionally formed on a metal level of an integrated circuit. The coil comprises four spirals between an external terminal E and an internal terminal S. Terminal S is connected to a switch I1 via a line l1 shown in dotted lines and performed on a metal level different from the metal level used to form the coil. Intermediary points P1 and P2, located in this example at the level of the second and third coil spiral, are respectively connected to switches I2 and I3 via lines l2 and l3 formed on a level different from that of the coil. Terminal E of the coil and the terminals of switches I1 to I3 non-connected to the coil are connected to connection terminals and possibly to elements of the integrated circuit on which is formed the coil.
A disadvantage of this inductance is that the presence of lines l1 to l3 between the coil and the switches causes parasitic effects in the coil.
Another disadvantage of this inductance is that when switch I2 or I3 is activated, the unused end of the coil located beyond point P1 or point P2 causes parasitic effects in the “useful” portion of the coil located between point E and point P1 or point P2.
Accordingly, such an inductance is not adapted to the provision of several inductance values due to parasitic phenomena.